Along with a rapid spread of portable wireless terminals over the last few years, there have been worldwide scarcities in available frequency resources. Further, along an increase in rich content and a growing diversity of services, there has been a growing market demand for large-capacity and high-speed communications. In response, for the expansion of frequencies available to the existing third-generation system (3G, 3rd Generation) and the adaptation to the next-generation system (LTE: Long Term Evolution) to handle large-capacity and high-speed communications, Mid-Band (1.5 GHz band for WCDMA Band IX) has become available to portable wireless terminals, in addition to the conventional Low-Band (800 to 900 MHz band for WCDMA, CMDA 2000, AMPS, EGSM, etc.) and High-Band (1700 to 2100 MHz band for WCDMA, CMDA 2000, DCS, PCS, etc.). Furthermore, as portable wireless terminals have become more and more multifunctional, the adaptation to various wireless communications systems, such as international roaming, One Seg (Japanese terrestrial digital broadcasting service for mobile devices) viewing, GPS, wireless LAN, Bluetooth, etc., has become essential. Under such circumstances, as for antennas that are built in portable wireless terminals, the placement of a plurality of antenna elements within a limited space has been required.
The placement of antenna elements at enough space from each other with respect to the wavelengths in the frequency bands to which the antenna elements respectively correspond makes it possible to suppress deterioration due to mutual interference between each antenna element and the other while securing the characteristics of each antenna element. However, for the realization of multifunctionality as mentioned above in addition to reductions in size and thickness of portable wireless terminals, it has become essential to place a plurality of antenna elements in a certain part within a wireless terminal.
In the case of a wireless terminal including an antenna composed of a plurality of antenna elements, i.e., in the case of a straight-type portable wireless terminal composed of a single housing, the antenna is usually placed in an edge portion of the housing that extends along a long side of the housing. In the case of a portable wireless terminal composed of two housings on the operation side and the display side and having a hinge section via which the two housing are rotatably connected to each other, such as a foldable portable wireless terminal or a biaxial-rotation portable wireless terminal, the antenna is usually placed in a region where a sizable space can be secured, such as the hinge section or an edge portion of the operation-side housing opposite the hinge. In so doing, the placement of each antenna element is very important in considering the characteristics of the antenna. In particular, in the case of a complex antenna including three antenna elements, it is very useful to provide a more preferable placement of each antenna element.
Patent Literature 1 discloses a conventional technology for placing three antenna elements in an identical space.